Fig. 4. ChIP analysis showing that H-NS inhibits ToxR binding to cis-acting elements upstream of leuO.

The toxRS/hns null mutant cells expressing strep-tagged ToxR were cross-linked, washed, and sonicated as described in Materials and Methods. Lysates were then treated with either anti-Strep-tag II monoclonal antibody or normal mouse IgG as a control. Free DNA was purified and analyzed by quantitative real-time PCR (qRT-PCR) on a Light Cycler 480 II real-time PCR system. Relative enrichment was calculated as the amount of transcript compared to the transcript from cells without L-arabinose. Values are averages from biological experiments done in triplicate. Error bars indicate standard deviations (**p < 0.005; NS, not significant in Student’s t test with p > 0.05).